Less lock acquisitions for AudioMixer.

webrtc/modules/audio_mixer/audio_mixer_impl.h

Index: webrtc/modules/audio_mixer/audio_mixer_impl.h
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.h b/webrtc/modules/audio_mixer/audio_mixer_impl.h
index 6ddf9ca5e8bde5c6954d458a6cfcdba8a902f9e7..5c1f11a58f07adf001d4ccae584d3033efaff3b2 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.h
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.h
@@ -32,7 +32,7 @@ struct FrameAndMuteInfo {
   bool muted;
 };

[kwiberg-webrtc, 2016/08/30 16:29:45]

Is this struct still used somewhere, or can you remove it?

 
-typedef std::list<FrameAndMuteInfo> AudioFrameList;
+typedef std::list<AudioFrame*> AudioFrameList;

[aleloi, 2016/08/30 15:13:34]

Mixing structure is a little simplified. Mute information is only used
inside of Get*AnonymousAudio. Muted frames are filtered out one step
earlier. Therefore a |muted| field is no longer needed here.

 typedef std::list<MixerAudioSource*> MixerAudioSourceList;
 
 // Cheshire cat implementation of MixerAudioSource's non virtual functions.
@@ -89,16 +89,11 @@ class AudioMixerImpl : public AudioMixer {
   // Compute what audio sources to mix from audio_source_list_. Ramp in
   // and out. Update mixed status. maxAudioFrameCounter specifies how
   // many participants are allowed to be mixed.

[kwiberg-webrtc, 2016/08/30 16:29:45]

This comment needs updating.

-  AudioFrameList UpdateToMix(size_t maxAudioFrameCounter) const;
+  AudioFrameList GetNonAnonymousAudio() const;
 
-  // Return the lowest mixing frequency that can be used without having to
-  // downsample any audio.
-  int32_t GetLowestMixingFrequency() const;
-  int32_t GetLowestMixingFrequencyFromList(
-      const MixerAudioSourceList& mixList) const;

[aleloi, 2016/08/30 15:13:34]

These two have not been used for the last 3-4 mixer changes.

-
-  // Return the AudioFrames that should be mixed anonymously.
-  void GetAdditionalAudio(AudioFrameList* additionalFramesList) const;
+  // Return the AudioFrames that should be mixed anonymously. Ramp in
+  // and out. Update mixed status.
+  AudioFrameList GetAnonymousAudio() const;

[aleloi, 2016/08/30 15:13:34]

Made naming and signature more consistent between the Get*Audio
methods.

 
   // This function returns true if it finds the MixerAudioSource in the
   // specified list of MixerAudioSources.
@@ -118,12 +113,6 @@ class AudioMixerImpl : public AudioMixer {
                              int32_t id,
                              bool use_limiter);
 
-  // Mix the AudioFrames stored in audioFrameList into mixedAudio. No
-  // record will be kept of this mix (e.g. the corresponding MixerAudioSources
-  // will not be marked as IsMixed()
-  int32_t MixAnonomouslyFromList(AudioFrame* mixedAudio,
-                                 const AudioFrameList& audioFrameList) const;
-

[aleloi, 2016/08/30 15:13:34]

Merged with MixFromList

   bool LimitMixedAudio(AudioFrame* mixedAudio) const;
 
   // Output level functions for VoEVolumeControl.
@@ -132,7 +121,6 @@ class AudioMixerImpl : public AudioMixer {
   int GetOutputAudioLevelFullRange() override;
 
   std::unique_ptr<CriticalSectionWrapper> crit_;
-  std::unique_ptr<CriticalSectionWrapper> cb_crit_;

[aleloi, 2016/08/30 15:13:34]

I think only one lock is needed. Adding/removing/querying status of
participants can happen on different threads. In addition the mixing
is done on another thread.

The public adding/removing/querying methods are all guarded by cb_crit_.

Getting audio from participants and updating participants mixing
history is all done guarded by cb_crit_. The other parts of mixing do
not hold locks. AFAIK this is enough, since the mixing is
done on a single thread.

 
   int32_t id_;
 
@@ -143,7 +131,7 @@ class AudioMixerImpl : public AudioMixer {
   // List of all audio sources. Note all lists are disjunct
   MixerAudioSourceList audio_source_list_;  // May be mixed.
 
-  // Always mixed, anonomously.
+  // Always mixed, anonymously.
   MixerAudioSourceList additional_audio_source_list_;
 
   size_t num_mixed_audio_sources_;
@@ -161,6 +149,8 @@ class AudioMixerImpl : public AudioMixer {
 
   // Measures audio level for the combined signal.
   voe::AudioLevel audio_level_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(AudioMixerImpl);
 };
 }  // namespace webrtc